What is an adverse drug reaction (ADR)?

An adverse drug reaction (ADR) is defined as a harmful or unintended reaction that occurs as a result of taking a medication. This can include a wide range of effects, from mild side effects that are unpleasant to severe reactions that could be life-threatening. The key aspect of an ADR is that it is not just any negative effect but specifically one that is associated with medication use, differentiating it from expected side effects or health improvements that might arise in response to a drug.

In contrast, beneficial effects or reactions that improve patient health are not classified as ADRs because they represent the intended therapeutic outcomes of a medication. Similarly, reactions that are expected side effects are also not considered ADRs since they are anticipated and understood by healthcare providers and patients alike. Therefore, the definition of an ADR hinges on the concept of harm and unintended occurrence associated with the use of medication, solidifying its categorization as a critical area of concern in pharmacology and patient safety.